Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 211733
AFDPQR

Area Forecast Discussion
National Weather Service Portland Oregon
933 AM PST Sat Jan 21 2017

.SYNOPSIS...Broad low pressure continues off the Pacific NW coast
this morning, with one last main band of showers moving through today
before the low moves north and weakens. The next low is developing
out near 40N/137W this morning and will be centered near bouy 5,
about 300 miles west of Astoria, by later tonight and Sunday. This
low will spread another band of rain and mountain snow across the
forecast area late tonight and Sunday morning. The low will move
south off California Monday with decreasing showers in our forecast
area. A very weak disturbance will drop south across the area and
maintain quite a bit of clouds in the area Tuesday, otherwise an
upper ridge will build in over the area for much of next week and
weaken any systems that try to approach.
&&

.SHORT TERM...Today through Monday...A 980 mb low remains off the
Washington and north Oregon coast this morning and will weaken and
move north through today. The last part of the trough axis will move
through today for one more round of decent showers, and as evident on
IR satellite imagery and National Weather Service Doppler radar this
shows up as a decent band of clouds and precipitation lifting
northeast across the area. The models show some 30 to 40 kt 850 mb
southwesterly winds that will provide a bit more enhancement to the
precipitation today than on Friday, especially on the Oregon side of
our forecast area. This will bring 2 to 5 inches of snow to the
Cascades, and possibly 1 to 3 or 4 inches of snow into early this
evening in the Gorge mainly east of Multnomah Falls and in the upper
Hood River Valley.

Precipitation eases for a while tonight, then increases again from
the southwest later tonight and Sunday morning as the next developing
low out near 40N/137W this morning deepens to around 960 mb along
130W near buoy 5 late tonight and Sunday. This spreads another
frontal band onshore from the southwest later tonight and Sunday
morning. Precipitation amounts look a little more broken up as this
band moves through, though we may get low end advisory type snow in
the Gorge and the Upper Hood River Valley again. The precipitation
turns to showers and decreases Sunday afternoon as the low remains
off the coast and there is not much onshore flow.

The low remains off the coast into Sunday night, then drops south to
off California later Monday and Monday night. This will cause showers
to decrease from the north Monday with some breaks in the clouds
likely to develop. Tolleson

.LONG TERM...No Changes. Previous discussion follows...
Monday night through Friday...As the low pressure system drops south
of our area Monday night, a large upper-level ridge builds over the
area. As the ridge moves in the GFS brings one last shortwave across
the area. The GFS is the only model with this feature, so right now
have left precipitation out of the forecast, though I did increase
cloud cover on Tuesday. Behind this, the ridge builds over the area
drying us out through Wednesday. GFS and ECMWF differ on how long the
dry spell will last.  The ECMWF is quicker with the next shortwave
trough which it brings into our area on Wednesday night. The GFS on
the other hand doesn`t bring our next system in until Thursday
night-Friday. Either way, expect easterly winds to develop ahead of
this next system. Right now snow levels look to stay up above 3000
feet. -McCoy
&&

.AVIATION...Mostly VFR conditions continue this morning, but coast
south of KTMK remains MVFR in steadier rain. More widespread rain
will move from south to north across region today, for lowering cigs
and reduced vsbys across region. Expect more widespread MVFR observed
18z-23z, though still not convinced it will be particularly lengthy
at any given terminal. Showers taper off 00z-06z with some
improvement, but next round of steadier rain arrives by 08z with
better chance of MVFR conditions across much of the region.

PDX AND APPROACHES...VFR cigs will gradually lower as next round of
rain arrives. Showers taper off after 00z through 06z for some
improvement, but next round of steadier rain will likely bring MVFR
cigs/vsbys again aft 12z. Cullen
&&

.MARINE...Low end small craft winds continue this morning for all
waters and should remain mostly consistent through mid day when winds
will increase associated with the next frontal wave moving through
the waters. Some guidance is indicating a brief period of gusts to
gale force during the early to mid afternoon period. Will forgo any
gale warning for today given the borderline wind speeds and the brief
(~3 hour) window of concern.

Winds will subside to low end small craft Saturday night and then
increase again during the day Sunday as a strong (sub-970mb) low
moves north and eventually settles off the Oregon shore. Gales appear
likely for most of the day Sunday at least for the outer waters, and
given the increased confidence have upgraded the gale watch to a
warning. Given the southeasterly component of the BL winds, not sure
if the inner waters will reach be as consistent with the stronger
winds, but gales likely to occur at least beyond about 5 nm from
shore. Seas remain 18 to 22 feet today and will gradually subside to
15 to 19 feet by late tonight, before building again a bit on Sunday
afternoon in response to strengthening winds. Seas then ease to 15
feet or so by early Monday morning.
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory until 10 PM PST this evening for Central
     Oregon Coast-North Oregon Coast.

     Winter Weather Advisory until 6 PM PST Sunday for Central
     Columbia River Gorge-Upper Hood River Valley-Western
     Columbia River Gorge.

WA...High Surf Advisory until 10 PM PST this evening for South
     Washington Coast.

     Winter Weather Advisory until 6 PM PST Sunday for Central
     Columbia River Gorge-Western Columbia River Gorge.

PZ...Small Craft Advisory for Rough Columbia River Bar until 3 PM
     PST Sunday.

     Small Craft Advisory for winds and hazardous seas until
     midnight PST tonight for Coastal Waters from Cape Shoalwater
     WA to Florence OR out 60 nm.

     Gale Warning from midnight tonight to 10 PM PST Sunday for
     Coastal Waters from Cape Shoalwater WA to Florence OR out
     60 nm.

&&

$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.



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